<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>重复请求问题</title>
</head>
<body>
    <button>点我发送请求哟</button>
    <script>
        // 获取元素对象
        const btns = document.querySelectorAll('button');
        let x = null;
        // 标识变量
        let isSending = false; // 是否正在发送AJAX请求

        btns[0].onclick = function(){
            // 判断标识变量
            if(isSending) x.abort(); // 正在发送则取消发送，创建新请求
            x = new XMLHttpRequest();
            // 修改标识变量值
            isSending = true;
            x.open("GET", 'http://127.0.0.1:8000/delay')
            x.send();
            x.onreadystatechange = function(){
                if(x.readyState === 4){
                    // 修改标识变量
                    isSending = false;
                }
            }
        }
    </script>
</body>
</html>